Light projectors are often used on theatrical stages to light entertainers. Some light projectors make use of patterns or electronic light valves to project images onto projection screens or stage surfaces.
U.S. Pat. No. 7,048,383, to Belliveau discloses a filter system method and states in its “Background of the Invention”: “During a theatrical presentation the Image projection lighting devices are often operated in conjunction with theatrical fog generating devices. The theatrical fog or smoke generating devices are used to create an airborne haze that can be used as a projection surface creating three dimensional imagery. The fog generating devices create the airborne haze by propelling minute particles into the air which can remain suspended in the air for a considerable time. The minute particles are commonly created by the fog generating devices by atomization of oils or glycols. The glycol or mineral oil particles (referred to herein as fog particles) can each range in size from between twenty microns to below 0.1 micron.
When lighting devices such as image projection lighting devices contain complex optical and electronic components the fog particles may be drawn though the cooling system and may condense on the various optical components diffusing the projected image or shortening the life of the components.” (U.S. Pat. No. 7,048,383 to Belliveau, col. 2, line 30-col. 2, line 49).
Filters systems like that disclosed in U.S. Pat. No. 7,048,383 to Belliveau amount to a considerable expense of a light projector when designing an economical light projector system. There is still a need however to prevent critical optical components from condensing with fog particles when by design no adequate filter system is incorporated into the product. Output lenses of image projection lighting devices, may typically have an inner surface that is located in the internal environment to a lamp housing and an external surface that is exposed an external environment of the lamp housing. Because there can be a temperature differential between the inner surface and the outer surface, theatrical fog haze can typically form condensate on the inner surface or even the outer surface. When the condensation forms on the lens the output light can become defused by the light scattering properties of the condensate. The output lens can be a lens having an optical power or a transparent output window.
More recent light projectors may comprise a light source of a solid state LED light source that emits less infrared energy than halogen or arc light sources making the problem of controlling condensation by theatrical haze even more difficult because the output lens absorbs less infrared energy from the light source and thus operates at a lower temperature.
There is a need to find a method of reducing condensate on at least one optical component of a light projector without using a costly filtration system.